In 1919, he was transferred to Section II (Intelligence) at the Lithuanian-Belarusian Front Headquarters, and later to the General Staff.

In 1929, he organized a teachers' union, Zrąb, and other educational societies, including the Polish Academy of Literature.

After Piłsudski's death in 1935, he opposed the Camp of National Unity (OZN, Ozon) and the right wing of the Sanacja movement, and retired from political life.

After the Soviet invasion during the Polish Defensive War of 1939, he fled to Romania and later through Palestine to London.

He was a brother of Wacław Jędrzejewicz and married Cezaria Baudouin de Courtenay Ehrenkreutz Jędrzejewiczowa, a pioneer of ethnography in Poland.